Support for a tube bundle

ABSTRACT

A support for a bundle of tubes, which support has more than one transverse support plates spaced apart along the direction of the tubes to be supported, and which support plates are provided with openings for accommodating the tubes, wherein the support plates are segmental baffle support elements and expanded metal support elements.

This application is a division of application Ser. No. 11/018,719, filedDec. 21, 2004, pending.

FIELD OF THE INVENTION

The present invention relates to a support for a bundle of tubes, inparticular to such a support comprising a plurality of transversesupport plates known as segmental baffles, which are spaced apart alongthe direction of the tubes to be supported.

BACKGROUND OF THE INVENTION

A major area of application of the tube bundle is in shell-and-tube heatexchangers. A shell-and-tube heat exchanger comprises a cylindricalvessel internally provided with a bundle of tubes that extend inlongitudinal direction of the vessel. The bundle of tubes can inparticular be a bundle of parallel tubes, and is also referred to as atube bundle.

As is well known, the shell-and-tube heat exchanger is an indirect heatexchanger in which heat is transferred between a fluid passing throughthe tubes of the tube bundle (the tube side) and a fluid passing throughthe space outside the tubes (the shell side). Details of theshell-and-tube heat exchanger can, for example, be found in Perry'sChemical Engineers' Handbook, 6^(th) edition, 1984, McGraw-Hill Inc.,page 11-3 to 11-21. The tube bundle is the most important part of theheat exchanger. The ends of the tubes are secured to a tube sheet. Theheat exchanger can include two tube sheets, one at each end of thecylindrical vessel, or a single tube sheet at one end of the cylindricalvessel in the event the heat exchanger is a U-tube exchanger.

It will be understood that the intermediate portions of the tubes haveto be supported as well, for example to prevent damage to the tubes dueto vibrations caused by the fluid flow. To support the intermediateportions of the tubes, a tube support normally comprises axially spacedapart transverse support plates. A support plate is sometimes alsoreferred to as a support sheet or a support baffle.

One type of support plate is a segmental baffle. Several kinds ofsegmental baffles are discussed in Perry's. Conventional segmentalbaffles are made of a circular metal plate from which a circle segment(“window”) is cut off, and through the remainder of the plate aplurality of openings is punched or cut through which the tubes canpass. Sometimes two circle segments are cut off at opposite sides, forexample for use in so-called double segmental baffle arrangements, or inno-tube-in-window arrangements.

Segmental baffles not only support the tubes, but also influence thefluid flow through the shell side. Therefore, the design of a baffle isalso determined by heat-transfer considerations. Segmental baffle tubesupports are used when a certain amount of cross-flow of fluid in theshell over the tube bundle is desired for reasons of optimizing heattransfer.

The design of segmental baffles can be adapted, within certain limits,to the specific requirements of a particular practical application. Forexample the so-called baffle cut can be specifically selected, which isthe percentage of the circle diameter which has been cut off to form thesegmental baffle. A large baffle cut in a single segmental baffleprovides a relatively low pressure drop, however the relatively largepart of the tubes that run through the window remains unsupported.Normally one tries to support a tube by at least every second segmentalbaffle, so that the maximum baffle cut that is normally adopted is 45%.

When tubes run through the windows, the maximum unsupported length of atube (“unsupported tube length”) is at least twice the spacing betweensegmental baffles. Therefore it is inherent with the segmental baffletube supports that the number of support plates is at least twice ofthat which would be required from a mechanical support point of viewalone. Segmental baffles contribute substantially to the cost of a heatexchanger, so one tries to maximize the spacing between baffles. Whenthe unsupported tube length becomes too large, this can lead tovibration problems.

In other heat exchanger designs no tubes run through the windows. Forexample, in very tall vertical heat exchangers (such as those which arereferred to as “Texas towers”, used e.g. as feed/effluent heatexchangers in large-scale industrial processes), single segmentalbaffles are commonly arranged at a certain spacing, with the windowsalternatingly at opposite sides in order to achieve a desired cross-flowpattern of the fluid over the tube bundle along the shell. Since thespacing that is desired for reasons of optimum fluid flow and optimumhydraulic performance (in particular minimum pressure drop) can be muchlonger than the spacing required for good mechanical support againstvibrations, a number of additional segmental support baffles, but withtwo windows each, are placed in between the single segmental baffles.These additional elements represent a considerable cost element of theentire tube support.

Japanese Patent Application with publication No. 05-296680 describes asupport baffle plate wherein a plurality of co-operating sheet metalstrips are arranged in the window to suppress vibration. Due to thespecial shape required for all individual sheet metal strips,manufacturing costs are high.

Tube supports consisting solely of expanded metal support elements aredisclosed in International Patent Application Publication No. WO03/067170. However, this publication does not refer to vibrationproblems in conventional segmental baffle heat exchangers.

It would be useful to provide a support for a bundle of tubes, whichallows a simpler, cheaper mechanical support against vibrations insegmental baffle tube supports.

SUMMARY OF THE INVENTION

The present invention is directed to a support for a bundle of tubes,which support comprises a plurality of transverse support plates spacedapart along the direction of the tubes to be supported, and which platesare provided with openings for accommodating the tubes, wherein theplurality of support plates comprises segmental baffle support elementsand expanded metal support elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically a longitudinal cross-section through a firstembodiment of a heat exchanger with support according to the presentinvention.

FIG. 2 shows schematically a cross section along II-II in FIG. 1.

FIG. 3 shows schematically a cross section along III-III in FIG. 1.

FIG. 4 shows schematically a segmental support baffle.

FIG. 5 shows schematically a combined support baffle formed of asegmental baffle support element and an expanded metal support element.

FIG. 6 shows schematically a longitudinal cross-section through a secondembodiment of a heat exchanger with support according to the presentinvention.

FIG. 7 shows schematically a cross section along VII-VII in FIG. 6.

FIG. 8 shows schematically a cross section along VIII-VIII in FIG. 6.

FIG. 9 shows schematically another segmental support baffle.

FIG. 10 shows schematically a conventional segmental baffle for use asintermediate support plate in a Texas tower.

FIG. 11 shows schematically an intermediate expanded metal support plateaccording to the invention.

FIG. 12 shows schematically a longitudinal cross-section through a thirdembodiment of a heat exchanger with support according to the presentinvention.

FIG. 13 shows schematically a further expanded metal support elementaccording to the invention.

Like reference numbers are used in the Figures to refer to the same orsimilar objects.

DETAILED DESCRIPTION OF THE INVENTION

Part of the mechanical support function in a segmental baffle tubesupport does not have to be provided by conventional segmental baffleelements, but may with advantage be provided by expanded metal elements.Expanded metal may be manufactured considerably more cheaply thansegmental baffles because less material is used, fewer cuttings areproduced, and less labor is required. The present invention allows thetube support to be designed such that the segmental baffles are placedwhere they are needed for reasons of fluid flow, as well as where theyalso provide mechanical support. Further mechanical support, inparticular to prevent vibrations, may be provided by expanded metalelements. Expanded metal influences fluid flow far less than aconventional segmental baffle.

The invention in this way allows far more flexibility in designingsegmental baffle heat exchangers. The basic design parameters of theheat exchanger like tube size and arrangement (e.g. triangular or squarepitch), shell diameter, segmental baffle size and spacing, may be chosenfor optimum fluid flow, heat transfer performance and pressure drop, notcompromised by vibration considerations. A vibration problem that mightbe encountered may, according to the invention, be solved by placingexpanded metal support elements.

The expression “support element” is used in the description and in theclaims to refer to a part of a support plate, or to a full supportplate.

Expanded metal and segmental baffle support elements together may form acombined support plate. To this end expanded metal may be arranged tospan the window(s) of the segmental baffle support element. In this waymechanical support may be provided over the full cross-section of thesupport plate, but fluid may only flow through the window. Since theexpanded metal also imposes some small flow restriction, it may bedesirable to slightly increase the size of the window compared to aconventional segmental support baffle.

Expanded metal support elements in the form of expanded metal supportplates may also be arranged between two segmental baffle supportelements, as an additional mechanical support.

In a further embodiment, the expanded metal support plate may have asegmental shape itself, i.e. one or more segments may be cut off so thatone or more windows are formed. This may be advantageous in designswhere no tubes run through the windows of segmental baffles, and whereadditional mechanical support between segmental baffles is desired witha minimum disturbance of fluid flow.

Reference is now made to FIGS. 1-5. FIG. 1 shows part of a verticalshell-and tube heat exchanger 1 in longitudinal cross-section, and FIGS.2 and 3 show two cross-sections along lines II-II and III-III,respectively. The heat exchanger 1 has a shell 3 and a bundle of tubes5, of which the tubes 8,9,10,11,12,13,14 are visible in FIG. 1. Thesupport for the tube bundle 5 comprises the four support plates18,19,20,21 shown in FIG. 1. The plates are spaced by a fixed distanceL₁ from each other along the length direction of the tubes 8-14.

Support plates 18,19 and 21 are conventional segmental baffles as shownenlarged in FIG. 4. These segmental baffles are manufactured from acircular plate 25 from which a segment has been cut off so that windowsare formed when mounted in the heat exchanger, e.g. window 28. Openings30 have been cut into the remaining plate 25.

Support plate 20 is a combined support plate, as shown in FIG. 5 in moredetail. The combined support plate 35 is formed of a segmental bafflesupport element 38 and an expanded metal support element 40 which spansthe window 42 left open by the segmental baffle support element 38. Theexpanded metal element 40 may for example be welded to the segmentalbaffle element 38 and to the strip 45 around the window 42. The strip 45itself may also be welded to the segmental baffle element, but may alsobe a remainder from the original circular plate from which the segmentalbaffle element 38 was formed by e.g. milling.

Expanded metal may be made by providing sheet metal with a structure ofslits followed by stretching the slit sheet metal. A structure ofcross-laths, formed of so-called strands and bonds, with interstices isformed. The arrangement and length of the slits as well as the extent ofstretching determines the size, shape and relative arrangement of theinterstices, which can therefore be designed such that the tubes canpass through them and are optimally supported.

Normally the strands between adjacent bonds are twisted out of the planeof the original sheet metal, which results in a lowering of therestriction to fluid flow normal to the sheet of expanded metal.

The support plate 20 mechanically supports the tubes over the fullcross-section of the shell 3, i.e. also in the window 42. Therefore, theunsupported tube length of tube 8 for example, between support plates 19and 21 is L₁. For comparison, the unsupported tube length of e.g. tube14 between support plates 18 and 20 is 2L₁. The invention may in thisway serve to decrease the unsupported tube length in order to suppressvibrations. If more or all support plates in the heat exchanger 1 werecombined support plates 35, it would be possible to increase the spacingbetween support plates from a mechanical point of view.

Reference is now made to FIGS. 6-11, and a second embodiment of thepresent invention will now be discussed.

FIG. 6 shows part of a Texas tower heat exchanger 101 in longitudinalcross-section, and FIGS. 7 and 8 show two cross-sections along linesVII-VII and VIII-VIII, respectively. The heat exchanger 101 has avertical cylindrical shell 103 and a bundle of tubes 105 running throughthe central part of the shell 103. The tubes 108,109 and 110 are visiblein FIG. 6. The Texas tower may for example have a height of 24 m and adiameter of 2.5 m.

The support for the tube bundle 105 comprises the five support plates117,118,119,120,121 shown in FIG. 6 as support elements. The plates arespaced from each other along the length direction of the tubes 108-110.

Support plates 117 and 121 are conventional segmental baffles 124 asshown enlarged in FIG. 9. These segmental baffles are manufactured froma circular plate 125 from which a segment has been cut off along line126 so that windows 127, 128 are formed when the respective plates aremounted in the heat exchanger 101. The windows are arranged at oppositesides in the heat exchanger as shown. Into the remaining plate 125openings 130 have been cut according to the size and arrangement of thetubes 105. No openings are arranged in the part 131 opposite to thewindow, since the design of the heat exchanger 101 as shown in FIG. 6 isa so-called no-tube-in-windows design.

The spacing L₂ between segmental baffles is chosen such that anoptimized fluid flow is obtained, wherein the flow passes through thewindows 127 and 128 thereby crossing the tube bundle 105. A typicalvalue for L₂ is 1.5 m. If the spacing L₂ is too large for preventingvibrations of the tubes, additional intermediate support plates aremounted in a conventional Texas tower, like the plate 133 shown in FIG.10. Plate 133 is a segmental support baffle which has two sections cutoff at opposite sides, and is provided with openings 134 for the tubes.Such additional intermediate support plates would be mounted e.g. at thesame locations as shown for plates 118, 119, 120, and such that thewindows register with the windows 127 and 128.

In the embodiment according to the invention as shown in FIGS. 6-8,however, the intermediate support plates 118, 119 and 120 are expandedmetal support plates, like the plate 135 schematically shown in FIG. 11.

The plate 135 is formed by a double segmental expanded metal sheet 136,which is welded to a support ring 138 and support strips 140 so as toform windows 142 and 143. Support plate 135 may be manufactured muchmore cheaply than a conventional intermediate plate 134 as shown in FIG.10.

Reference is now made to FIGS. 12-13, and with reference to these Figs.a third embodiment of the invention will be discussed.

The horizontal heat exchanger 201 with shell 203 through which the tubebundle 205 runs is an example of such a design. FIG. 12 shows part of alongitudinal cross-section, and it will be understood that the heatexchanger may be much longer, and that more support plates than shownmay be arranged. The tube bundle 205 includes tubes 208, 209, 210, 211,212, 213, and 214. The Figure does not show the end parts of the tubeswith the tube sheet.

The tubes are supported by segmental baffles 218, 219, 220. As furthersupport against tube vibrations expanded metal support plates 221,222are arranged. The segmental baffle support elements and the expandedmetal support elements are alternatingly arranged at a fixed spacingalong the length direction of the tubes 205. The spacing betweenadjacent segmental baffles, e.g. 218 and 219, is L₃.

The segmental baffle support elements 218, 219, 220 are similar to thoseshown and described with reference to FIG. 4. Halfway in betweenadjacent segmental baffles, an expanded metal support plate like theplate 235 shown in FIG. 13 is arranged. The plate 235 may be cheaplymanufactured, for example, by cutting a sheet of expanded metal tocircular shape, e.g. by laser cutting, and welding to a support ring245.

The expanded metal support plates 221,222 serve to prevent vibrationsbetween segmental baffles. The maximum unsupported tube length of e.g.tube 214 is L₃, equal to the spacing between adjacent segmental baffles.Without the expanded metal support elements the unsupported tube lengthwould be twice the spacing between adjacent segmental baffles. In thisway, the present invention allows the spacing between adjacent segmentalbaffles to be larger than if the tube support were made of segmentalbaffles only. The segmental baffles may thus be placed such that optimumfluid flow in the shell side and heat transfer is achieved, and theoverall cost of the tube support may be minimized.

However, in some applications it may also happen that tube vibrationconsiderations pose a limitation on the minimum spacing betweensegmental baffles. This may be the case when it is desired to maximizecross-flow of fluid in the shell, in order to maximize heat transfer ina given heat exchanger volume. In this case, segmental baffles of lowbaffle cut are used, and it is desirable to minimize the spacing betweenthe baffles. This results in a large pressure drop, but may alsogenerate tube vibrations despite the relatively short spacing betweensegmental baffles. In such a situation it would previously have beenneeded to increase the baffle spacing and possibly increase the size ofthe heat exchanger. With the present invention, however, additionalexpanded metal support plates can solve the vibration problem. Althoughthe cost of the tube support in the heat exchanger slightly increases bythe use of the additional expanded metal support elements, the totalcost of the heat exchanger may be lower because a smaller shell may beused.

It shall be clear that the present invention can equally be applied tohorizontal and vertical heat exchangers.

The support plates may be mounted in any suitable way in the shell. Aconventional method for mounting segmental baffles is to use spacer rodsarranged parallel to the tubes, which are welded to the shell and to thesegmental baffles. Such rods may likewise be welded to the support ringof expanded metal support elements.

For many applications of the present invention the expanded metalsupport elements suitably have interstices with a size just large enoughsuch that the tubes may be passed through, so that each tube issupported from four sides substantially without play. Typically in thiscase the size would be such that at maximum, a gauge of 10% largerdiameter than the tube could pass through the interstices. This size ofinterstices is for example preferred for the embodiments discussed withreference to FIGS. 1 and 12, wherein each expanded metal support elementpreferably supports the tubes sufficiently.

It will be clear however that it is also possible to use expanded metalwith interstices so large that several tubes can pass through. In thiscase suitably several sheets of expanded metal are arranged toco-operate so that the tubes are supported from all sides, for examplethe intermediate expanded metals support elements of the embodimentdiscussed with reference to FIG. 6. Suitable such arrangements ofseveral expanded metal sheets are discussed in WO 03/067170. Othersuitable arrangements, types of expanded metal and arrangement andshapes of interstices of expanded metal are described in European Patentapplication No. 03077463.2, unpublished at the first filing (priority)date of the present invention.

1. A heat exchanger comprising a bundle of tubes supported by aplurality of support elements transverse to and spaced apart along thedirection of the tubes to be supported, said plurality of supportelements comprising at least one double segmental expanded metal supportelement.
 2. The heat exchanger of claim 1, wherein said plurality ofsupport elements additionally comprises at least one single segmentalbaffle support element.
 3. The heat exchanger of claim 2, wherein two ofthe plurality of support elements are single segmental baffle supportelements and as least one double segmental expanded metal supportelement is arranged intermediate thereto.
 4. The heat exchanger of claim1, wherein said heat exchanger comprises a vertical heat exchanger. 5.The heat exchanger of claim 4, wherein a plurality of double segmentalexpanded metal support elements are arranged intermediate to two singlesegmental baffle support elements
 6. The heat exchanger of claim 1,wherein the double segmental expanded metal support element is formedfrom a double segmental metal sheet, which is welded to a support ringand support strips so as to form a double segmental expanded metalsupport element having two windows.
 7. The heat exchanger of claim 5,wherein each of the plurality of double segmental expanded metal supportelements is formed from a double segmental metal sheet, which is weldedto a support ring and support strips so as to form a double segmentalexpanded metal support element having two windows.
 8. The heat exchangerof claim 7, wherein there are no tubes in the windows formed by thesingle segmental baffle support elements or the double segmentalexpanded metal support elements.
 9. The heat exchanger of claim 8,wherein said heat exchanger comprises a vertical heat exchanger.
 10. Theheat exchanger of claim 5, wherein the spacing between the singlesegmental baffle support elements is approximately 1.5 meters.